source: rtems-graphics-toolkit/jpeg-7/transupp.c @ 2abf143

/*
 * transupp.c
 *
 * Copyright (C) 1997-2009, Thomas G. Lane, Guido Vollbeding.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains image transformation routines and other utility code
 * used by the jpegtran sample application.  These are NOT part of the core
 * JPEG library.  But we keep these routines separate from jpegtran.c to
 * ease the task of maintaining jpegtran-like programs that have other user
 * interfaces.
 */

/* Although this file really shouldn't have access to the library internals,
 * it's helpful to let it call jround_up() and jcopy_block_row().
 */
#define JPEG_INTERNALS

#include "jinclude.h"
#include "jpeglib.h"
#include "transupp.h"           /* My own external interface */
#include <ctype.h>              /* to declare isdigit() */


#if TRANSFORMS_SUPPORTED

/*
 * Lossless image transformation routines.  These routines work on DCT
 * coefficient arrays and thus do not require any lossy decompression
 * or recompression of the image.
 * Thanks to Guido Vollbeding for the initial design and code of this feature,
 * and to Ben Jackson for introducing the cropping feature.
 *
 * Horizontal flipping is done in-place, using a single top-to-bottom
 * pass through the virtual source array.  It will thus be much the
 * fastest option for images larger than main memory.
 *
 * The other routines require a set of destination virtual arrays, so they
 * need twice as much memory as jpegtran normally does.  The destination
 * arrays are always written in normal scan order (top to bottom) because
 * the virtual array manager expects this.  The source arrays will be scanned
 * in the corresponding order, which means multiple passes through the source
 * arrays for most of the transforms.  That could result in much thrashing
 * if the image is larger than main memory.
 *
 * If cropping or trimming is involved, the destination arrays may be smaller
 * than the source arrays.  Note it is not possible to do horizontal flip
 * in-place when a nonzero Y crop offset is specified, since we'd have to move
 * data from one block row to another but the virtual array manager doesn't
 * guarantee we can touch more than one row at a time.  So in that case,
 * we have to use a separate destination array.
 *
 * Some notes about the operating environment of the individual transform
 * routines:
 * 1. Both the source and destination virtual arrays are allocated from the
 *    source JPEG object, and therefore should be manipulated by calling the
 *    source's memory manager.
 * 2. The destination's component count should be used.  It may be smaller
 *    than the source's when forcing to grayscale.
 * 3. Likewise the destination's sampling factors should be used.  When
 *    forcing to grayscale the destination's sampling factors will be all 1,
 *    and we may as well take that as the effective iMCU size.
 * 4. When "trim" is in effect, the destination's dimensions will be the
 *    trimmed values but the source's will be untrimmed.
 * 5. When "crop" is in effect, the destination's dimensions will be the
 *    cropped values but the source's will be uncropped.  Each transform
 *    routine is responsible for picking up source data starting at the
 *    correct X and Y offset for the crop region.  (The X and Y offsets
 *    passed to the transform routines are measured in iMCU blocks of the
 *    destination.)
 * 6. All the routines assume that the source and destination buffers are
 *    padded out to a full iMCU boundary.  This is true, although for the
 *    source buffer it is an undocumented property of jdcoefct.c.
 */


LOCAL(void)
do_crop (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
         JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
         jvirt_barray_ptr *src_coef_arrays,
         jvirt_barray_ptr *dst_coef_arrays)
/* Crop.  This is only used when no rotate/flip is requested with the crop. */
{
  JDIMENSION dst_blk_y, x_crop_blocks, y_crop_blocks;
  int ci, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  jpeg_component_info *compptr;

  /* We simply have to copy the right amount of data (the destination's
   * image size) starting at the given X and Y offsets in the source.
   */
  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      src_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, src_coef_arrays[ci],
         dst_blk_y + y_crop_blocks,
         (JDIMENSION) compptr->v_samp_factor, FALSE);
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        jcopy_block_row(src_buffer[offset_y] + x_crop_blocks,
                        dst_buffer[offset_y],
                        compptr->width_in_blocks);
      }
    }
  }
}


LOCAL(void)
do_flip_h_no_crop (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
                   JDIMENSION x_crop_offset,
                   jvirt_barray_ptr *src_coef_arrays)
/* Horizontal flip; done in-place, so no separate dest array is required.
 * NB: this only works when y_crop_offset is zero.
 */
{
  JDIMENSION MCU_cols, comp_width, blk_x, blk_y, x_crop_blocks;
  int ci, k, offset_y;
  JBLOCKARRAY buffer;
  JCOEFPTR ptr1, ptr2;
  JCOEF temp1, temp2;
  jpeg_component_info *compptr;

  /* Horizontal mirroring of DCT blocks is accomplished by swapping
   * pairs of blocks in-place.  Within a DCT block, we perform horizontal
   * mirroring by changing the signs of odd-numbered columns.
   * Partial iMCUs at the right edge are left untouched.
   */
  MCU_cols = srcinfo->image_width / (dstinfo->max_h_samp_factor * DCTSIZE);

  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    comp_width = MCU_cols * compptr->h_samp_factor;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    for (blk_y = 0; blk_y < compptr->height_in_blocks;
         blk_y += compptr->v_samp_factor) {
      buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, src_coef_arrays[ci], blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        /* Do the mirroring */
        for (blk_x = 0; blk_x * 2 < comp_width; blk_x++) {
          ptr1 = buffer[offset_y][blk_x];
          ptr2 = buffer[offset_y][comp_width - blk_x - 1];
          /* this unrolled loop doesn't need to know which row it's on... */
          for (k = 0; k < DCTSIZE2; k += 2) {
            temp1 = *ptr1;      /* swap even column */
            temp2 = *ptr2;
            *ptr1++ = temp2;
            *ptr2++ = temp1;
            temp1 = *ptr1;      /* swap odd column with sign change */
            temp2 = *ptr2;
            *ptr1++ = -temp2;
            *ptr2++ = -temp1;
          }
        }
        if (x_crop_blocks > 0) {
          /* Now left-justify the portion of the data to be kept.
           * We can't use a single jcopy_block_row() call because that routine
           * depends on memcpy(), whose behavior is unspecified for overlapping
           * source and destination areas.  Sigh.
           */
          for (blk_x = 0; blk_x < compptr->width_in_blocks; blk_x++) {
            jcopy_block_row(buffer[offset_y] + blk_x + x_crop_blocks,
                            buffer[offset_y] + blk_x,
                            (JDIMENSION) 1);
          }
        }
      }
    }
  }
}


LOCAL(void)
do_flip_h (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
           JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
           jvirt_barray_ptr *src_coef_arrays,
           jvirt_barray_ptr *dst_coef_arrays)
/* Horizontal flip in general cropping case */
{
  JDIMENSION MCU_cols, comp_width, dst_blk_x, dst_blk_y;
  JDIMENSION x_crop_blocks, y_crop_blocks;
  int ci, k, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  JBLOCKROW src_row_ptr, dst_row_ptr;
  JCOEFPTR src_ptr, dst_ptr;
  jpeg_component_info *compptr;

  /* Here we must output into a separate array because we can't touch
   * different rows of a single virtual array simultaneously.  Otherwise,
   * this is essentially the same as the routine above.
   */
  MCU_cols = srcinfo->image_width / (dstinfo->max_h_samp_factor * DCTSIZE);

  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    comp_width = MCU_cols * compptr->h_samp_factor;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      src_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, src_coef_arrays[ci],
         dst_blk_y + y_crop_blocks,
         (JDIMENSION) compptr->v_samp_factor, FALSE);
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        dst_row_ptr = dst_buffer[offset_y];
        src_row_ptr = src_buffer[offset_y];
        for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks; dst_blk_x++) {
          if (x_crop_blocks + dst_blk_x < comp_width) {
            /* Do the mirrorable blocks */
            dst_ptr = dst_row_ptr[dst_blk_x];
            src_ptr = src_row_ptr[comp_width - x_crop_blocks - dst_blk_x - 1];
            /* this unrolled loop doesn't need to know which row it's on... */
            for (k = 0; k < DCTSIZE2; k += 2) {
              *dst_ptr++ = *src_ptr++;   /* copy even column */
              *dst_ptr++ = - *src_ptr++; /* copy odd column with sign change */
            }
          } else {
            /* Copy last partial block(s) verbatim */
            jcopy_block_row(src_row_ptr + dst_blk_x + x_crop_blocks,
                            dst_row_ptr + dst_blk_x,
                            (JDIMENSION) 1);
          }
        }
      }
    }
  }
}


LOCAL(void)
do_flip_v (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
           JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
           jvirt_barray_ptr *src_coef_arrays,
           jvirt_barray_ptr *dst_coef_arrays)
/* Vertical flip */
{
  JDIMENSION MCU_rows, comp_height, dst_blk_x, dst_blk_y;
  JDIMENSION x_crop_blocks, y_crop_blocks;
  int ci, i, j, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  JBLOCKROW src_row_ptr, dst_row_ptr;
  JCOEFPTR src_ptr, dst_ptr;
  jpeg_component_info *compptr;

  /* We output into a separate array because we can't touch different
   * rows of the source virtual array simultaneously.  Otherwise, this
   * is a pretty straightforward analog of horizontal flip.
   * Within a DCT block, vertical mirroring is done by changing the signs
   * of odd-numbered rows.
   * Partial iMCUs at the bottom edge are copied verbatim.
   */
  MCU_rows = srcinfo->image_height / (dstinfo->max_v_samp_factor * DCTSIZE);

  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    comp_height = MCU_rows * compptr->v_samp_factor;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      if (y_crop_blocks + dst_blk_y < comp_height) {
        /* Row is within the mirrorable area. */
        src_buffer = (*srcinfo->mem->access_virt_barray)
          ((j_common_ptr) srcinfo, src_coef_arrays[ci],
           comp_height - y_crop_blocks - dst_blk_y -
           (JDIMENSION) compptr->v_samp_factor,
           (JDIMENSION) compptr->v_samp_factor, FALSE);
      } else {
        /* Bottom-edge blocks will be copied verbatim. */
        src_buffer = (*srcinfo->mem->access_virt_barray)
          ((j_common_ptr) srcinfo, src_coef_arrays[ci],
           dst_blk_y + y_crop_blocks,
           (JDIMENSION) compptr->v_samp_factor, FALSE);
      }
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        if (y_crop_blocks + dst_blk_y < comp_height) {
          /* Row is within the mirrorable area. */
          dst_row_ptr = dst_buffer[offset_y];
          src_row_ptr = src_buffer[compptr->v_samp_factor - offset_y - 1];
          src_row_ptr += x_crop_blocks;
          for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks;
               dst_blk_x++) {
            dst_ptr = dst_row_ptr[dst_blk_x];
            src_ptr = src_row_ptr[dst_blk_x];
            for (i = 0; i < DCTSIZE; i += 2) {
              /* copy even row */
              for (j = 0; j < DCTSIZE; j++)
                *dst_ptr++ = *src_ptr++;
              /* copy odd row with sign change */
              for (j = 0; j < DCTSIZE; j++)
                *dst_ptr++ = - *src_ptr++;
            }
          }
        } else {
          /* Just copy row verbatim. */
          jcopy_block_row(src_buffer[offset_y] + x_crop_blocks,
                          dst_buffer[offset_y],
                          compptr->width_in_blocks);
        }
      }
    }
  }
}


LOCAL(void)
do_transpose (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
              JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
              jvirt_barray_ptr *src_coef_arrays,
              jvirt_barray_ptr *dst_coef_arrays)
/* Transpose source into destination */
{
  JDIMENSION dst_blk_x, dst_blk_y, x_crop_blocks, y_crop_blocks;
  int ci, i, j, offset_x, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  JCOEFPTR src_ptr, dst_ptr;
  jpeg_component_info *compptr;

  /* Transposing pixels within a block just requires transposing the
   * DCT coefficients.
   * Partial iMCUs at the edges require no special treatment; we simply
   * process all the available DCT blocks for every component.
   */
  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks;
             dst_blk_x += compptr->h_samp_factor) {
          src_buffer = (*srcinfo->mem->access_virt_barray)
            ((j_common_ptr) srcinfo, src_coef_arrays[ci],
             dst_blk_x + x_crop_blocks,
             (JDIMENSION) compptr->h_samp_factor, FALSE);
          for (offset_x = 0; offset_x < compptr->h_samp_factor; offset_x++) {
            dst_ptr = dst_buffer[offset_y][dst_blk_x + offset_x];
            src_ptr = src_buffer[offset_x][dst_blk_y + offset_y + y_crop_blocks];
            for (i = 0; i < DCTSIZE; i++)
              for (j = 0; j < DCTSIZE; j++)
                dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
          }
        }
      }
    }
  }
}


LOCAL(void)
do_rot_90 (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
           JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
           jvirt_barray_ptr *src_coef_arrays,
           jvirt_barray_ptr *dst_coef_arrays)
/* 90 degree rotation is equivalent to
 *   1. Transposing the image;
 *   2. Horizontal mirroring.
 * These two steps are merged into a single processing routine.
 */
{
  JDIMENSION MCU_cols, comp_width, dst_blk_x, dst_blk_y;
  JDIMENSION x_crop_blocks, y_crop_blocks;
  int ci, i, j, offset_x, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  JCOEFPTR src_ptr, dst_ptr;
  jpeg_component_info *compptr;

  /* Because of the horizontal mirror step, we can't process partial iMCUs
   * at the (output) right edge properly.  They just get transposed and
   * not mirrored.
   */
  MCU_cols = srcinfo->image_height / (dstinfo->max_h_samp_factor * DCTSIZE);

  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    comp_width = MCU_cols * compptr->h_samp_factor;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks;
             dst_blk_x += compptr->h_samp_factor) {
          if (x_crop_blocks + dst_blk_x < comp_width) {
            /* Block is within the mirrorable area. */
            src_buffer = (*srcinfo->mem->access_virt_barray)
              ((j_common_ptr) srcinfo, src_coef_arrays[ci],
               comp_width - x_crop_blocks - dst_blk_x -
               (JDIMENSION) compptr->h_samp_factor,
               (JDIMENSION) compptr->h_samp_factor, FALSE);
          } else {
            /* Edge blocks are transposed but not mirrored. */
            src_buffer = (*srcinfo->mem->access_virt_barray)
              ((j_common_ptr) srcinfo, src_coef_arrays[ci],
               dst_blk_x + x_crop_blocks,
               (JDIMENSION) compptr->h_samp_factor, FALSE);
          }
          for (offset_x = 0; offset_x < compptr->h_samp_factor; offset_x++) {
            dst_ptr = dst_buffer[offset_y][dst_blk_x + offset_x];
            if (x_crop_blocks + dst_blk_x < comp_width) {
              /* Block is within the mirrorable area. */
              src_ptr = src_buffer[compptr->h_samp_factor - offset_x - 1]
                [dst_blk_y + offset_y + y_crop_blocks];
              for (i = 0; i < DCTSIZE; i++) {
                for (j = 0; j < DCTSIZE; j++)
                  dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
                i++;
                for (j = 0; j < DCTSIZE; j++)
                  dst_ptr[j*DCTSIZE+i] = -src_ptr[i*DCTSIZE+j];
              }
            } else {
              /* Edge blocks are transposed but not mirrored. */
              src_ptr = src_buffer[offset_x]
                [dst_blk_y + offset_y + y_crop_blocks];
              for (i = 0; i < DCTSIZE; i++)
                for (j = 0; j < DCTSIZE; j++)
                  dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
            }
          }
        }
      }
    }
  }
}


LOCAL(void)
do_rot_270 (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
            JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
            jvirt_barray_ptr *src_coef_arrays,
            jvirt_barray_ptr *dst_coef_arrays)
/* 270 degree rotation is equivalent to
 *   1. Horizontal mirroring;
 *   2. Transposing the image.
 * These two steps are merged into a single processing routine.
 */
{
  JDIMENSION MCU_rows, comp_height, dst_blk_x, dst_blk_y;
  JDIMENSION x_crop_blocks, y_crop_blocks;
  int ci, i, j, offset_x, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  JCOEFPTR src_ptr, dst_ptr;
  jpeg_component_info *compptr;

  /* Because of the horizontal mirror step, we can't process partial iMCUs
   * at the (output) bottom edge properly.  They just get transposed and
   * not mirrored.
   */
  MCU_rows = srcinfo->image_width / (dstinfo->max_v_samp_factor * DCTSIZE);

  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    comp_height = MCU_rows * compptr->v_samp_factor;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks;
             dst_blk_x += compptr->h_samp_factor) {
          src_buffer = (*srcinfo->mem->access_virt_barray)
            ((j_common_ptr) srcinfo, src_coef_arrays[ci],
             dst_blk_x + x_crop_blocks,
             (JDIMENSION) compptr->h_samp_factor, FALSE);
          for (offset_x = 0; offset_x < compptr->h_samp_factor; offset_x++) {
            dst_ptr = dst_buffer[offset_y][dst_blk_x + offset_x];
            if (y_crop_blocks + dst_blk_y < comp_height) {
              /* Block is within the mirrorable area. */
              src_ptr = src_buffer[offset_x]
                [comp_height - y_crop_blocks - dst_blk_y - offset_y - 1];
              for (i = 0; i < DCTSIZE; i++) {
                for (j = 0; j < DCTSIZE; j++) {
                  dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
                  j++;
                  dst_ptr[j*DCTSIZE+i] = -src_ptr[i*DCTSIZE+j];
                }
              }
            } else {
              /* Edge blocks are transposed but not mirrored. */
              src_ptr = src_buffer[offset_x]
                [dst_blk_y + offset_y + y_crop_blocks];
              for (i = 0; i < DCTSIZE; i++)
                for (j = 0; j < DCTSIZE; j++)
                  dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
            }
          }
        }
      }
    }
  }
}


LOCAL(void)
do_rot_180 (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
            JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
            jvirt_barray_ptr *src_coef_arrays,
            jvirt_barray_ptr *dst_coef_arrays)
/* 180 degree rotation is equivalent to
 *   1. Vertical mirroring;
 *   2. Horizontal mirroring.
 * These two steps are merged into a single processing routine.
 */
{
  JDIMENSION MCU_cols, MCU_rows, comp_width, comp_height, dst_blk_x, dst_blk_y;
  JDIMENSION x_crop_blocks, y_crop_blocks;
  int ci, i, j, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  JBLOCKROW src_row_ptr, dst_row_ptr;
  JCOEFPTR src_ptr, dst_ptr;
  jpeg_component_info *compptr;

  MCU_cols = srcinfo->image_width / (dstinfo->max_h_samp_factor * DCTSIZE);
  MCU_rows = srcinfo->image_height / (dstinfo->max_v_samp_factor * DCTSIZE);

  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    comp_width = MCU_cols * compptr->h_samp_factor;
    comp_height = MCU_rows * compptr->v_samp_factor;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      if (y_crop_blocks + dst_blk_y < comp_height) {
        /* Row is within the vertically mirrorable area. */
        src_buffer = (*srcinfo->mem->access_virt_barray)
          ((j_common_ptr) srcinfo, src_coef_arrays[ci],
           comp_height - y_crop_blocks - dst_blk_y -
           (JDIMENSION) compptr->v_samp_factor,
           (JDIMENSION) compptr->v_samp_factor, FALSE);
      } else {
        /* Bottom-edge rows are only mirrored horizontally. */
        src_buffer = (*srcinfo->mem->access_virt_barray)
          ((j_common_ptr) srcinfo, src_coef_arrays[ci],
           dst_blk_y + y_crop_blocks,
           (JDIMENSION) compptr->v_samp_factor, FALSE);
      }
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        dst_row_ptr = dst_buffer[offset_y];
        if (y_crop_blocks + dst_blk_y < comp_height) {
          /* Row is within the mirrorable area. */
          src_row_ptr = src_buffer[compptr->v_samp_factor - offset_y - 1];
          for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks; dst_blk_x++) {
            dst_ptr = dst_row_ptr[dst_blk_x];
            if (x_crop_blocks + dst_blk_x < comp_width) {
              /* Process the blocks that can be mirrored both ways. */
              src_ptr = src_row_ptr[comp_width - x_crop_blocks - dst_blk_x - 1];
              for (i = 0; i < DCTSIZE; i += 2) {
                /* For even row, negate every odd column. */
                for (j = 0; j < DCTSIZE; j += 2) {
                  *dst_ptr++ = *src_ptr++;
                  *dst_ptr++ = - *src_ptr++;
                }
                /* For odd row, negate every even column. */
                for (j = 0; j < DCTSIZE; j += 2) {
                  *dst_ptr++ = - *src_ptr++;
                  *dst_ptr++ = *src_ptr++;
                }
              }
            } else {
              /* Any remaining right-edge blocks are only mirrored vertically. */
              src_ptr = src_row_ptr[x_crop_blocks + dst_blk_x];
              for (i = 0; i < DCTSIZE; i += 2) {
                for (j = 0; j < DCTSIZE; j++)
                  *dst_ptr++ = *src_ptr++;
                for (j = 0; j < DCTSIZE; j++)
                  *dst_ptr++ = - *src_ptr++;
              }
            }
          }
        } else {
          /* Remaining rows are just mirrored horizontally. */
          src_row_ptr = src_buffer[offset_y];
          for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks; dst_blk_x++) {
            if (x_crop_blocks + dst_blk_x < comp_width) {
              /* Process the blocks that can be mirrored. */
              dst_ptr = dst_row_ptr[dst_blk_x];
              src_ptr = src_row_ptr[comp_width - x_crop_blocks - dst_blk_x - 1];
              for (i = 0; i < DCTSIZE2; i += 2) {
                *dst_ptr++ = *src_ptr++;
                *dst_ptr++ = - *src_ptr++;
              }
            } else {
              /* Any remaining right-edge blocks are only copied. */
              jcopy_block_row(src_row_ptr + dst_blk_x + x_crop_blocks,
                              dst_row_ptr + dst_blk_x,
                              (JDIMENSION) 1);
            }
          }
        }
      }
    }
  }
}


LOCAL(void)
do_transverse (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
               JDIMENSION x_crop_offset, JDIMENSION y_crop_offset,
               jvirt_barray_ptr *src_coef_arrays,
               jvirt_barray_ptr *dst_coef_arrays)
/* Transverse transpose is equivalent to
 *   1. 180 degree rotation;
 *   2. Transposition;
 * or
 *   1. Horizontal mirroring;
 *   2. Transposition;
 *   3. Horizontal mirroring.
 * These steps are merged into a single processing routine.
 */
{
  JDIMENSION MCU_cols, MCU_rows, comp_width, comp_height, dst_blk_x, dst_blk_y;
  JDIMENSION x_crop_blocks, y_crop_blocks;
  int ci, i, j, offset_x, offset_y;
  JBLOCKARRAY src_buffer, dst_buffer;
  JCOEFPTR src_ptr, dst_ptr;
  jpeg_component_info *compptr;

  MCU_cols = srcinfo->image_height / (dstinfo->max_h_samp_factor * DCTSIZE);
  MCU_rows = srcinfo->image_width / (dstinfo->max_v_samp_factor * DCTSIZE);

  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    comp_width = MCU_cols * compptr->h_samp_factor;
    comp_height = MCU_rows * compptr->v_samp_factor;
    x_crop_blocks = x_crop_offset * compptr->h_samp_factor;
    y_crop_blocks = y_crop_offset * compptr->v_samp_factor;
    for (dst_blk_y = 0; dst_blk_y < compptr->height_in_blocks;
         dst_blk_y += compptr->v_samp_factor) {
      dst_buffer = (*srcinfo->mem->access_virt_barray)
        ((j_common_ptr) srcinfo, dst_coef_arrays[ci], dst_blk_y,
         (JDIMENSION) compptr->v_samp_factor, TRUE);
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
        for (dst_blk_x = 0; dst_blk_x < compptr->width_in_blocks;
             dst_blk_x += compptr->h_samp_factor) {
          if (x_crop_blocks + dst_blk_x < comp_width) {
            /* Block is within the mirrorable area. */
            src_buffer = (*srcinfo->mem->access_virt_barray)
              ((j_common_ptr) srcinfo, src_coef_arrays[ci],
               comp_width - x_crop_blocks - dst_blk_x -
               (JDIMENSION) compptr->h_samp_factor,
               (JDIMENSION) compptr->h_samp_factor, FALSE);
          } else {
            src_buffer = (*srcinfo->mem->access_virt_barray)
              ((j_common_ptr) srcinfo, src_coef_arrays[ci],
               dst_blk_x + x_crop_blocks,
               (JDIMENSION) compptr->h_samp_factor, FALSE);
          }
          for (offset_x = 0; offset_x < compptr->h_samp_factor; offset_x++) {
            dst_ptr = dst_buffer[offset_y][dst_blk_x + offset_x];
            if (y_crop_blocks + dst_blk_y < comp_height) {
              if (x_crop_blocks + dst_blk_x < comp_width) {
                /* Block is within the mirrorable area. */
                src_ptr = src_buffer[compptr->h_samp_factor - offset_x - 1]
                  [comp_height - y_crop_blocks - dst_blk_y - offset_y - 1];
                for (i = 0; i < DCTSIZE; i++) {
                  for (j = 0; j < DCTSIZE; j++) {
                    dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
                    j++;
                    dst_ptr[j*DCTSIZE+i] = -src_ptr[i*DCTSIZE+j];
                  }
                  i++;
                  for (j = 0; j < DCTSIZE; j++) {
                    dst_ptr[j*DCTSIZE+i] = -src_ptr[i*DCTSIZE+j];
                    j++;
                    dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
                  }
                }
              } else {
                /* Right-edge blocks are mirrored in y only */
                src_ptr = src_buffer[offset_x]
                  [comp_height - y_crop_blocks - dst_blk_y - offset_y - 1];
                for (i = 0; i < DCTSIZE; i++) {
                  for (j = 0; j < DCTSIZE; j++) {
                    dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
                    j++;
                    dst_ptr[j*DCTSIZE+i] = -src_ptr[i*DCTSIZE+j];
                  }
                }
              }
            } else {
              if (x_crop_blocks + dst_blk_x < comp_width) {
                /* Bottom-edge blocks are mirrored in x only */
                src_ptr = src_buffer[compptr->h_samp_factor - offset_x - 1]
                  [dst_blk_y + offset_y + y_crop_blocks];
                for (i = 0; i < DCTSIZE; i++) {
                  for (j = 0; j < DCTSIZE; j++)
                    dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
                  i++;
                  for (j = 0; j < DCTSIZE; j++)
                    dst_ptr[j*DCTSIZE+i] = -src_ptr[i*DCTSIZE+j];
                }
              } else {
                /* At lower right corner, just transpose, no mirroring */
                src_ptr = src_buffer[offset_x]
                  [dst_blk_y + offset_y + y_crop_blocks];
                for (i = 0; i < DCTSIZE; i++)
                  for (j = 0; j < DCTSIZE; j++)
                    dst_ptr[j*DCTSIZE+i] = src_ptr[i*DCTSIZE+j];
              }
            }
          }
        }
      }
    }
  }
}


/* Parse an unsigned integer: subroutine for jtransform_parse_crop_spec.
 * Returns TRUE if valid integer found, FALSE if not.
 * *strptr is advanced over the digit string, and *result is set to its value.
 */

LOCAL(boolean)
jt_read_integer (const char ** strptr, JDIMENSION * result)
{
  const char * ptr = *strptr;
  JDIMENSION val = 0;

  for (; isdigit(*ptr); ptr++) {
    val = val * 10 + (JDIMENSION) (*ptr - '0');
  }
  *result = val;
  if (ptr == *strptr)
    return FALSE;               /* oops, no digits */
  *strptr = ptr;
  return TRUE;
}


/* Parse a crop specification (written in X11 geometry style).
 * The routine returns TRUE if the spec string is valid, FALSE if not.
 *
 * The crop spec string should have the format
 *      <width>x<height>{+-}<xoffset>{+-}<yoffset>
 * where width, height, xoffset, and yoffset are unsigned integers.
 * Each of the elements can be omitted to indicate a default value.
 * (A weakness of this style is that it is not possible to omit xoffset
 * while specifying yoffset, since they look alike.)
 *
 * This code is loosely based on XParseGeometry from the X11 distribution.
 */

GLOBAL(boolean)
jtransform_parse_crop_spec (jpeg_transform_info *info, const char *spec)
{
  info->crop = FALSE;
  info->crop_width_set = JCROP_UNSET;
  info->crop_height_set = JCROP_UNSET;
  info->crop_xoffset_set = JCROP_UNSET;
  info->crop_yoffset_set = JCROP_UNSET;

  if (isdigit(*spec)) {
    /* fetch width */
    if (! jt_read_integer(&spec, &info->crop_width))
      return FALSE;
    info->crop_width_set = JCROP_POS;
  }
  if (*spec == 'x' || *spec == 'X') {   
    /* fetch height */
    spec++;
    if (! jt_read_integer(&spec, &info->crop_height))
      return FALSE;
    info->crop_height_set = JCROP_POS;
  }
  if (*spec == '+' || *spec == '-') {
    /* fetch xoffset */
    info->crop_xoffset_set = (*spec == '-') ? JCROP_NEG : JCROP_POS;
    spec++;
    if (! jt_read_integer(&spec, &info->crop_xoffset))
      return FALSE;
  }
  if (*spec == '+' || *spec == '-') {
    /* fetch yoffset */
    info->crop_yoffset_set = (*spec == '-') ? JCROP_NEG : JCROP_POS;
    spec++;
    if (! jt_read_integer(&spec, &info->crop_yoffset))
      return FALSE;
  }
  /* We had better have gotten to the end of the string. */
  if (*spec != '\0')
    return FALSE;
  info->crop = TRUE;
  return TRUE;
}


/* Trim off any partial iMCUs on the indicated destination edge */

LOCAL(void)
trim_right_edge (jpeg_transform_info *info, JDIMENSION full_width)
{
  JDIMENSION MCU_cols;

  MCU_cols = info->output_width / (info->max_h_samp_factor * DCTSIZE);
  if (MCU_cols > 0 && info->x_crop_offset + MCU_cols ==
      full_width / (info->max_h_samp_factor * DCTSIZE))
    info->output_width = MCU_cols * (info->max_h_samp_factor * DCTSIZE);
}

LOCAL(void)
trim_bottom_edge (jpeg_transform_info *info, JDIMENSION full_height)
{
  JDIMENSION MCU_rows;

  MCU_rows = info->output_height / (info->max_v_samp_factor * DCTSIZE);
  if (MCU_rows > 0 && info->y_crop_offset + MCU_rows ==
      full_height / (info->max_v_samp_factor * DCTSIZE))
    info->output_height = MCU_rows * (info->max_v_samp_factor * DCTSIZE);
}


/* Request any required workspace.
 *
 * This routine figures out the size that the output image will be
 * (which implies that all the transform parameters must be set before
 * it is called).
 *
 * We allocate the workspace virtual arrays from the source decompression
 * object, so that all the arrays (both the original data and the workspace)
 * will be taken into account while making memory management decisions.
 * Hence, this routine must be called after jpeg_read_header (which reads
 * the image dimensions) and before jpeg_read_coefficients (which realizes
 * the source's virtual arrays).
 */

GLOBAL(void)
jtransform_request_workspace (j_decompress_ptr srcinfo,
                              jpeg_transform_info *info)
{
  jvirt_barray_ptr *coef_arrays = NULL;
  boolean need_workspace, transpose_it;
  jpeg_component_info *compptr;
  JDIMENSION xoffset, yoffset, width_in_iMCUs, height_in_iMCUs;
  JDIMENSION width_in_blocks, height_in_blocks;
  int ci, h_samp_factor, v_samp_factor;

  /* Determine number of components in output image */
  if (info->force_grayscale &&
      srcinfo->jpeg_color_space == JCS_YCbCr &&
      srcinfo->num_components == 3) {
    /* We'll only process the first component */
    info->num_components = 1;
  } else {
    /* Process all the components */
    info->num_components = srcinfo->num_components;
  }
  /* If there is only one output component, force the iMCU size to be 1;
   * else use the source iMCU size.  (This allows us to do the right thing
   * when reducing color to grayscale, and also provides a handy way of
   * cleaning up "funny" grayscale images whose sampling factors are not 1x1.)
   */

  switch (info->transform) {
  case JXFORM_TRANSPOSE:
  case JXFORM_TRANSVERSE:
  case JXFORM_ROT_90:
  case JXFORM_ROT_270:
    info->output_width = srcinfo->image_height;
    info->output_height = srcinfo->image_width;
    if (info->num_components == 1) {
      info->max_h_samp_factor = 1;
      info->max_v_samp_factor = 1;
    } else {
      info->max_h_samp_factor = srcinfo->max_v_samp_factor;
      info->max_v_samp_factor = srcinfo->max_h_samp_factor;
    }
    break;
  default:
    info->output_width = srcinfo->image_width;
    info->output_height = srcinfo->image_height;
    if (info->num_components == 1) {
      info->max_h_samp_factor = 1;
      info->max_v_samp_factor = 1;
    } else {
      info->max_h_samp_factor = srcinfo->max_h_samp_factor;
      info->max_v_samp_factor = srcinfo->max_v_samp_factor;
    }
    break;
  }

  /* If cropping has been requested, compute the crop area's position and
   * dimensions, ensuring that its upper left corner falls at an iMCU boundary.
   */
  if (info->crop) {
    /* Insert default values for unset crop parameters */
    if (info->crop_xoffset_set == JCROP_UNSET)
      info->crop_xoffset = 0;   /* default to +0 */
    if (info->crop_yoffset_set == JCROP_UNSET)
      info->crop_yoffset = 0;   /* default to +0 */
    if (info->crop_xoffset >= info->output_width ||
        info->crop_yoffset >= info->output_height)
      ERREXIT(srcinfo, JERR_BAD_CROP_SPEC);
    if (info->crop_width_set == JCROP_UNSET)
      info->crop_width = info->output_width - info->crop_xoffset;
    if (info->crop_height_set == JCROP_UNSET)
      info->crop_height = info->output_height - info->crop_yoffset;
    /* Ensure parameters are valid */
    if (info->crop_width <= 0 || info->crop_width > info->output_width ||
        info->crop_height <= 0 || info->crop_height > info->output_height ||
        info->crop_xoffset > info->output_width - info->crop_width ||
        info->crop_yoffset > info->output_height - info->crop_height)
      ERREXIT(srcinfo, JERR_BAD_CROP_SPEC);
    /* Convert negative crop offsets into regular offsets */
    if (info->crop_xoffset_set == JCROP_NEG)
      xoffset = info->output_width - info->crop_width - info->crop_xoffset;
    else
      xoffset = info->crop_xoffset;
    if (info->crop_yoffset_set == JCROP_NEG)
      yoffset = info->output_height - info->crop_height - info->crop_yoffset;
    else
      yoffset = info->crop_yoffset;
    /* Now adjust so that upper left corner falls at an iMCU boundary */
    info->output_width =
      info->crop_width + (xoffset % (info->max_h_samp_factor * DCTSIZE));
    info->output_height =
      info->crop_height + (yoffset % (info->max_v_samp_factor * DCTSIZE));
    /* Save x/y offsets measured in iMCUs */
    info->x_crop_offset = xoffset / (info->max_h_samp_factor * DCTSIZE);
    info->y_crop_offset = yoffset / (info->max_v_samp_factor * DCTSIZE);
  } else {
    info->x_crop_offset = 0;
    info->y_crop_offset = 0;
  }

  /* Figure out whether we need workspace arrays,
   * and if so whether they are transposed relative to the source.
   */
  need_workspace = FALSE;
  transpose_it = FALSE;
  switch (info->transform) {
  case JXFORM_NONE:
    if (info->x_crop_offset != 0 || info->y_crop_offset != 0)
      need_workspace = TRUE;
    /* No workspace needed if neither cropping nor transforming */
    break;
  case JXFORM_FLIP_H:
    if (info->trim)
      trim_right_edge(info, srcinfo->image_width);
    if (info->y_crop_offset != 0)
      need_workspace = TRUE;
    /* do_flip_h_no_crop doesn't need a workspace array */
    break;
  case JXFORM_FLIP_V:
    if (info->trim)
      trim_bottom_edge(info, srcinfo->image_height);
    /* Need workspace arrays having same dimensions as source image. */
    need_workspace = TRUE;
    break;
  case JXFORM_TRANSPOSE:
    /* transpose does NOT have to trim anything */
    /* Need workspace arrays having transposed dimensions. */
    need_workspace = TRUE;
    transpose_it = TRUE;
    break;
  case JXFORM_TRANSVERSE:
    if (info->trim) {
      trim_right_edge(info, srcinfo->image_height);
      trim_bottom_edge(info, srcinfo->image_width);
    }
    /* Need workspace arrays having transposed dimensions. */
    need_workspace = TRUE;
    transpose_it = TRUE;
    break;
  case JXFORM_ROT_90:
    if (info->trim)
      trim_right_edge(info, srcinfo->image_height);
    /* Need workspace arrays having transposed dimensions. */
    need_workspace = TRUE;
    transpose_it = TRUE;
    break;
  case JXFORM_ROT_180:
    if (info->trim) {
      trim_right_edge(info, srcinfo->image_width);
      trim_bottom_edge(info, srcinfo->image_height);
    }
    /* Need workspace arrays having same dimensions as source image. */
    need_workspace = TRUE;
    break;
  case JXFORM_ROT_270:
    if (info->trim)
      trim_bottom_edge(info, srcinfo->image_width);
    /* Need workspace arrays having transposed dimensions. */
    need_workspace = TRUE;
    transpose_it = TRUE;
    break;
  }

  /* Allocate workspace if needed.
   * Note that we allocate arrays padded out to the next iMCU boundary,
   * so that transform routines need not worry about missing edge blocks.
   */
  if (need_workspace) {
    coef_arrays = (jvirt_barray_ptr *)
      (*srcinfo->mem->alloc_small) ((j_common_ptr) srcinfo, JPOOL_IMAGE,
                SIZEOF(jvirt_barray_ptr) * info->num_components);
    width_in_iMCUs = (JDIMENSION)
      jdiv_round_up((long) info->output_width,
                    (long) (info->max_h_samp_factor * DCTSIZE));
    height_in_iMCUs = (JDIMENSION)
      jdiv_round_up((long) info->output_height,
                    (long) (info->max_v_samp_factor * DCTSIZE));
    for (ci = 0; ci < info->num_components; ci++) {
      compptr = srcinfo->comp_info + ci;
      if (info->num_components == 1) {
        /* we're going to force samp factors to 1x1 in this case */
        h_samp_factor = v_samp_factor = 1;
      } else if (transpose_it) {
        h_samp_factor = compptr->v_samp_factor;
        v_samp_factor = compptr->h_samp_factor;
      } else {
        h_samp_factor = compptr->h_samp_factor;
        v_samp_factor = compptr->v_samp_factor;
      }
      width_in_blocks = width_in_iMCUs * h_samp_factor;
      height_in_blocks = height_in_iMCUs * v_samp_factor;
      coef_arrays[ci] = (*srcinfo->mem->request_virt_barray)
        ((j_common_ptr) srcinfo, JPOOL_IMAGE, FALSE,
         width_in_blocks, height_in_blocks, (JDIMENSION) v_samp_factor);
    }
  }

  info->workspace_coef_arrays = coef_arrays;
}


/* Transpose destination image parameters */

LOCAL(void)
transpose_critical_parameters (j_compress_ptr dstinfo)
{
  int tblno, i, j, ci, itemp;
  jpeg_component_info *compptr;
  JQUANT_TBL *qtblptr;
  UINT16 qtemp;

  /* Transpose sampling factors */
  for (ci = 0; ci < dstinfo->num_components; ci++) {
    compptr = dstinfo->comp_info + ci;
    itemp = compptr->h_samp_factor;
    compptr->h_samp_factor = compptr->v_samp_factor;
    compptr->v_samp_factor = itemp;
  }

  /* Transpose quantization tables */
  for (tblno = 0; tblno < NUM_QUANT_TBLS; tblno++) {
    qtblptr = dstinfo->quant_tbl_ptrs[tblno];
    if (qtblptr != NULL) {
      for (i = 0; i < DCTSIZE; i++) {
        for (j = 0; j < i; j++) {
          qtemp = qtblptr->quantval[i*DCTSIZE+j];
          qtblptr->quantval[i*DCTSIZE+j] = qtblptr->quantval[j*DCTSIZE+i];
          qtblptr->quantval[j*DCTSIZE+i] = qtemp;
        }
      }
    }
  }
}


/* Adjust Exif image parameters.
 *
 * We try to adjust the Tags ExifImageWidth and ExifImageHeight if possible.
 */

LOCAL(void)
adjust_exif_parameters (JOCTET FAR * data, unsigned int length,
                        JDIMENSION new_width, JDIMENSION new_height)
{
  boolean is_motorola; /* Flag for byte order */
  unsigned int number_of_tags, tagnum;
  unsigned int firstoffset, offset;
  JDIMENSION new_value;

  if (length < 12) return; /* Length of an IFD entry */

  /* Discover byte order */
  if (GETJOCTET(data[0]) == 0x49 && GETJOCTET(data[1]) == 0x49)
    is_motorola = FALSE;
  else if (GETJOCTET(data[0]) == 0x4D && GETJOCTET(data[1]) == 0x4D)
    is_motorola = TRUE;
  else
    return;

  /* Check Tag Mark */
  if (is_motorola) {
    if (GETJOCTET(data[2]) != 0) return;
    if (GETJOCTET(data[3]) != 0x2A) return;
  } else {
    if (GETJOCTET(data[3]) != 0) return;
    if (GETJOCTET(data[2]) != 0x2A) return;
  }

  /* Get first IFD offset (offset to IFD0) */
  if (is_motorola) {
    if (GETJOCTET(data[4]) != 0) return;
    if (GETJOCTET(data[5]) != 0) return;
    firstoffset = GETJOCTET(data[6]);
    firstoffset <<= 8;
    firstoffset += GETJOCTET(data[7]);
  } else {
    if (GETJOCTET(data[7]) != 0) return;
    if (GETJOCTET(data[6]) != 0) return;
    firstoffset = GETJOCTET(data[5]);
    firstoffset <<= 8;
    firstoffset += GETJOCTET(data[4]);
  }
  if (firstoffset > length - 2) return; /* check end of data segment */

  /* Get the number of directory entries contained in this IFD */
  if (is_motorola) {
    number_of_tags = GETJOCTET(data[firstoffset]);
    number_of_tags <<= 8;
    number_of_tags += GETJOCTET(data[firstoffset+1]);
  } else {
    number_of_tags = GETJOCTET(data[firstoffset+1]);
    number_of_tags <<= 8;
    number_of_tags += GETJOCTET(data[firstoffset]);
  }
  if (number_of_tags == 0) return;
  firstoffset += 2;

  /* Search for ExifSubIFD offset Tag in IFD0 */
  for (;;) {
    if (firstoffset > length - 12) return; /* check end of data segment */
    /* Get Tag number */
    if (is_motorola) {
      tagnum = GETJOCTET(data[firstoffset]);
      tagnum <<= 8;
      tagnum += GETJOCTET(data[firstoffset+1]);
    } else {
      tagnum = GETJOCTET(data[firstoffset+1]);
      tagnum <<= 8;
      tagnum += GETJOCTET(data[firstoffset]);
    }
    if (tagnum == 0x8769) break; /* found ExifSubIFD offset Tag */
    if (--number_of_tags == 0) return;
    firstoffset += 12;
  }

  /* Get the ExifSubIFD offset */
  if (is_motorola) {
    if (GETJOCTET(data[firstoffset+8]) != 0) return;
    if (GETJOCTET(data[firstoffset+9]) != 0) return;
    offset = GETJOCTET(data[firstoffset+10]);
    offset <<= 8;
    offset += GETJOCTET(data[firstoffset+11]);
  } else {
    if (GETJOCTET(data[firstoffset+11]) != 0) return;
    if (GETJOCTET(data[firstoffset+10]) != 0) return;
    offset = GETJOCTET(data[firstoffset+9]);
    offset <<= 8;
    offset += GETJOCTET(data[firstoffset+8]);
  }
  if (offset > length - 2) return; /* check end of data segment */

  /* Get the number of directory entries contained in this SubIFD */
  if (is_motorola) {
    number_of_tags = GETJOCTET(data[offset]);
    number_of_tags <<= 8;
    number_of_tags += GETJOCTET(data[offset+1]);
  } else {
    number_of_tags = GETJOCTET(data[offset+1]);
    number_of_tags <<= 8;
    number_of_tags += GETJOCTET(data[offset]);
  }
  if (number_of_tags < 2) return;
  offset += 2;

  /* Search for ExifImageWidth and ExifImageHeight Tags in this SubIFD */
  do {
    if (offset > length - 12) return; /* check end of data segment */
    /* Get Tag number */
    if (is_motorola) {
      tagnum = GETJOCTET(data[offset]);
      tagnum <<= 8;
      tagnum += GETJOCTET(data[offset+1]);
    } else {
      tagnum = GETJOCTET(data[offset+1]);
      tagnum <<= 8;
      tagnum += GETJOCTET(data[offset]);
    }
    if (tagnum == 0xA002 || tagnum == 0xA003) {
      if (tagnum == 0xA002)
        new_value = new_width; /* ExifImageWidth Tag */
      else
        new_value = new_height; /* ExifImageHeight Tag */
      if (is_motorola) {
        data[offset+2] = 0; /* Format = unsigned long (4 octets) */
        data[offset+3] = 4;
        data[offset+4] = 0; /* Number Of Components = 1 */
        data[offset+5] = 0;
        data[offset+6] = 0;
        data[offset+7] = 1;
        data[offset+8] = 0;
        data[offset+9] = 0;
        data[offset+10] = (JOCTET)((new_value >> 8) & 0xFF);
        data[offset+11] = (JOCTET)(new_value & 0xFF);
      } else {
        data[offset+2] = 4; /* Format = unsigned long (4 octets) */
        data[offset+3] = 0;
        data[offset+4] = 1; /* Number Of Components = 1 */
        data[offset+5] = 0;
        data[offset+6] = 0;
        data[offset+7] = 0;
        data[offset+8] = (JOCTET)(new_value & 0xFF);
        data[offset+9] = (JOCTET)((new_value >> 8) & 0xFF);
        data[offset+10] = 0;
        data[offset+11] = 0;
      }
    }
    offset += 12;
  } while (--number_of_tags);
}


/* Adjust output image parameters as needed.
 *
 * This must be called after jpeg_copy_critical_parameters()
 * and before jpeg_write_coefficients().
 *
 * The return value is the set of virtual coefficient arrays to be written
 * (either the ones allocated by jtransform_request_workspace, or the
 * original source data arrays).  The caller will need to pass this value
 * to jpeg_write_coefficients().
 */

GLOBAL(jvirt_barray_ptr *)
jtransform_adjust_parameters (j_decompress_ptr srcinfo,
                              j_compress_ptr dstinfo,
                              jvirt_barray_ptr *src_coef_arrays,
                              jpeg_transform_info *info)
{
  /* If force-to-grayscale is requested, adjust destination parameters */
  if (info->force_grayscale) {
    /* First, ensure we have YCbCr or grayscale data, and that the source's
     * Y channel is full resolution.  (No reasonable person would make Y
     * be less than full resolution, so actually coping with that case
     * isn't worth extra code space.  But we check it to avoid crashing.)
     */
    if (((dstinfo->jpeg_color_space == JCS_YCbCr &&
          dstinfo->num_components == 3) ||
         (dstinfo->jpeg_color_space == JCS_GRAYSCALE &&
          dstinfo->num_components == 1)) &&
        srcinfo->comp_info[0].h_samp_factor == srcinfo->max_h_samp_factor &&
        srcinfo->comp_info[0].v_samp_factor == srcinfo->max_v_samp_factor) {
      /* We use jpeg_set_colorspace to make sure subsidiary settings get fixed
       * properly.  Among other things, it sets the target h_samp_factor &
       * v_samp_factor to 1, which typically won't match the source.
       * We have to preserve the source's quantization table number, however.
       */
      int sv_quant_tbl_no = dstinfo->comp_info[0].quant_tbl_no;
      jpeg_set_colorspace(dstinfo, JCS_GRAYSCALE);
      dstinfo->comp_info[0].quant_tbl_no = sv_quant_tbl_no;
    } else {
      /* Sorry, can't do it */
      ERREXIT(dstinfo, JERR_CONVERSION_NOTIMPL);
    }
  } else if (info->num_components == 1) {
    /* For a single-component source, we force the destination sampling factors
     * to 1x1, with or without force_grayscale.  This is useful because some
     * decoders choke on grayscale images with other sampling factors.
     */
    dstinfo->comp_info[0].h_samp_factor = 1;
    dstinfo->comp_info[0].v_samp_factor = 1;
  }

  /* Correct the destination's image dimensions as necessary
   * for crop and rotate/flip operations.
   */
  dstinfo->image_width = info->output_width;
  dstinfo->image_height = info->output_height;

  /* Transpose destination image parameters */
  switch (info->transform) {
  case JXFORM_TRANSPOSE:
  case JXFORM_TRANSVERSE:
  case JXFORM_ROT_90:
  case JXFORM_ROT_270:
    transpose_critical_parameters(dstinfo);
    break;
  default:
    break;
  }

  /* Adjust Exif properties */
  if (srcinfo->marker_list != NULL &&
      srcinfo->marker_list->marker == JPEG_APP0+1 &&
      srcinfo->marker_list->data_length >= 6 &&
      GETJOCTET(srcinfo->marker_list->data[0]) == 0x45 &&
      GETJOCTET(srcinfo->marker_list->data[1]) == 0x78 &&
      GETJOCTET(srcinfo->marker_list->data[2]) == 0x69 &&
      GETJOCTET(srcinfo->marker_list->data[3]) == 0x66 &&
      GETJOCTET(srcinfo->marker_list->data[4]) == 0 &&
      GETJOCTET(srcinfo->marker_list->data[5]) == 0) {
    /* Suppress output of JFIF marker */
    dstinfo->write_JFIF_header = FALSE;
    /* Adjust Exif image parameters */
    if (dstinfo->image_width != srcinfo->image_width ||
        dstinfo->image_height != srcinfo->image_height)
      /* Align data segment to start of TIFF structure for parsing */
      adjust_exif_parameters(srcinfo->marker_list->data + 6,
        srcinfo->marker_list->data_length - 6,
        dstinfo->image_width, dstinfo->image_height);
  }

  /* Return the appropriate output data set */
  if (info->workspace_coef_arrays != NULL)
    return info->workspace_coef_arrays;
  return src_coef_arrays;
}


/* Execute the actual transformation, if any.
 *
 * This must be called *after* jpeg_write_coefficients, because it depends
 * on jpeg_write_coefficients to have computed subsidiary values such as
 * the per-component width and height fields in the destination object.
 *
 * Note that some transformations will modify the source data arrays!
 */

GLOBAL(void)
jtransform_execute_transform (j_decompress_ptr srcinfo,
                              j_compress_ptr dstinfo,
                              jvirt_barray_ptr *src_coef_arrays,
                              jpeg_transform_info *info)
{
  jvirt_barray_ptr *dst_coef_arrays = info->workspace_coef_arrays;

  /* Note: conditions tested here should match those in switch statement
   * in jtransform_request_workspace()
   */
  switch (info->transform) {
  case JXFORM_NONE:
    if (info->x_crop_offset != 0 || info->y_crop_offset != 0)
      do_crop(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
              src_coef_arrays, dst_coef_arrays);
    break;
  case JXFORM_FLIP_H:
    if (info->y_crop_offset != 0)
      do_flip_h(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
                src_coef_arrays, dst_coef_arrays);
    else
      do_flip_h_no_crop(srcinfo, dstinfo, info->x_crop_offset,
                        src_coef_arrays);
    break;
  case JXFORM_FLIP_V:
    do_flip_v(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
              src_coef_arrays, dst_coef_arrays);
    break;
  case JXFORM_TRANSPOSE:
    do_transpose(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
                 src_coef_arrays, dst_coef_arrays);
    break;
  case JXFORM_TRANSVERSE:
    do_transverse(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
                  src_coef_arrays, dst_coef_arrays);
    break;
  case JXFORM_ROT_90:
    do_rot_90(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
              src_coef_arrays, dst_coef_arrays);
    break;
  case JXFORM_ROT_180:
    do_rot_180(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
               src_coef_arrays, dst_coef_arrays);
    break;
  case JXFORM_ROT_270:
    do_rot_270(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
               src_coef_arrays, dst_coef_arrays);
    break;
  }
}

/* jtransform_perfect_transform
 *
 * Determine whether lossless transformation is perfectly
 * possible for a specified image and transformation.
 *
 * Inputs:
 *   image_width, image_height: source image dimensions.
 *   MCU_width, MCU_height: pixel dimensions of MCU.
 *   transform: transformation identifier.
 * Parameter sources from initialized jpeg_struct
 * (after reading source header):
 *   image_width = cinfo.image_width
 *   image_height = cinfo.image_height
 *   MCU_width = cinfo.max_h_samp_factor * DCTSIZE
 *   MCU_height = cinfo.max_v_samp_factor * DCTSIZE
 * Result:
 *   TRUE = perfect transformation possible
 *   FALSE = perfect transformation not possible
 *           (may use custom action then)
 */

GLOBAL(boolean)
jtransform_perfect_transform(JDIMENSION image_width, JDIMENSION image_height,
                             int MCU_width, int MCU_height,
                             JXFORM_CODE transform)
{
  boolean result = TRUE; /* initialize TRUE */

  switch (transform) {
  case JXFORM_FLIP_H:
  case JXFORM_ROT_270:
    if (image_width % (JDIMENSION) MCU_width)
      result = FALSE;
    break;
  case JXFORM_FLIP_V:
  case JXFORM_ROT_90:
    if (image_height % (JDIMENSION) MCU_height)
      result = FALSE;
    break;
  case JXFORM_TRANSVERSE:
  case JXFORM_ROT_180:
    if (image_width % (JDIMENSION) MCU_width)
      result = FALSE;
    if (image_height % (JDIMENSION) MCU_height)
      result = FALSE;
    break;
  default:
    break;
  }

  return result;
}

#endif /* TRANSFORMS_SUPPORTED */


/* Setup decompression object to save desired markers in memory.
 * This must be called before jpeg_read_header() to have the desired effect.
 */

GLOBAL(void)
jcopy_markers_setup (j_decompress_ptr srcinfo, JCOPY_OPTION option)
{
#ifdef SAVE_MARKERS_SUPPORTED
  int m;

  /* Save comments except under NONE option */
  if (option != JCOPYOPT_NONE) {
    jpeg_save_markers(srcinfo, JPEG_COM, 0xFFFF);
  }
  /* Save all types of APPn markers iff ALL option */
  if (option == JCOPYOPT_ALL) {
    for (m = 0; m < 16; m++)
      jpeg_save_markers(srcinfo, JPEG_APP0 + m, 0xFFFF);
  }
#endif /* SAVE_MARKERS_SUPPORTED */
}

/* Copy markers saved in the given source object to the destination object.
 * This should be called just after jpeg_start_compress() or
 * jpeg_write_coefficients().
 * Note that those routines will have written the SOI, and also the
 * JFIF APP0 or Adobe APP14 markers if selected.
 */

GLOBAL(void)
jcopy_markers_execute (j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
                       JCOPY_OPTION option)
{
  jpeg_saved_marker_ptr marker;

  /* In the current implementation, we don't actually need to examine the
   * option flag here; we just copy everything that got saved.
   * But to avoid confusion, we do not output JFIF and Adobe APP14 markers
   * if the encoder library already wrote one.
   */
  for (marker = srcinfo->marker_list; marker != NULL; marker = marker->next) {
    if (dstinfo->write_JFIF_header &&
        marker->marker == JPEG_APP0 &&
        marker->data_length >= 5 &&
        GETJOCTET(marker->data[0]) == 0x4A &&
        GETJOCTET(marker->data[1]) == 0x46 &&
        GETJOCTET(marker->data[2]) == 0x49 &&
        GETJOCTET(marker->data[3]) == 0x46 &&
        GETJOCTET(marker->data[4]) == 0)
      continue;                 /* reject duplicate JFIF */
    if (dstinfo->write_Adobe_marker &&
        marker->marker == JPEG_APP0+14 &&
        marker->data_length >= 5 &&
        GETJOCTET(marker->data[0]) == 0x41 &&
        GETJOCTET(marker->data[1]) == 0x64 &&
        GETJOCTET(marker->data[2]) == 0x6F &&
        GETJOCTET(marker->data[3]) == 0x62 &&
        GETJOCTET(marker->data[4]) == 0x65)
      continue;                 /* reject duplicate Adobe */
#ifdef NEED_FAR_POINTERS
    /* We could use jpeg_write_marker if the data weren't FAR... */
    {
      unsigned int i;
      jpeg_write_m_header(dstinfo, marker->marker, marker->data_length);
      for (i = 0; i < marker->data_length; i++)
        jpeg_write_m_byte(dstinfo, marker->data[i]);
    }
#else
    jpeg_write_marker(dstinfo, marker->marker,
                      marker->data, marker->data_length);
#endif
  }
}